Create image with ASCII chars ordered by intensity

AsciiArtGenerator

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.util.*;

/**
 * Create an ASCII letters sorted by intensity. By including the inverse letters 
 * the number of combinations are increased.
 *
 * The input is expected to be a file with ascii letters organized in 16x16.
 *
 * An example of such image is:
 * http://www3.telus.net/anapan8/8x16%20font%20ASCII%20DOS%20437.gif
 * http://www3.telus.net/anapan8/8x8%20font%20ASCII%20DOS%20437.gif
 */
public class AsciiArtGenerator {
    public static void main(String[] args) {
        if (args.length != 2){
            System.out.println("Usage [input] [output]");
            System.exit(-1);
        }
        try{
            BufferedImage bufferedImage = ImageIO.read(new File(args[0]));
            int width = bufferedImage.getWidth()/16;
            int height = bufferedImage.getHeight()/16;
            Vector<BufferedImage> subImages = new Vector<BufferedImage>();
            for (int i=0;i<16;i++){
                for (int j=0;j<16;j++){
                    BufferedImage subImage = bufferedImage.getSubimage(i * width, j * height, width, height);
                    subImages.add(subImage);
                    BufferedImage invImg = getInverseImage(subImage);
                    subImages.add(invImg);
                }
            }

            Collections.sort(subImages, new Comparator<BufferedImage>() {
                public int compare(BufferedImage b1, BufferedImage b2) {
                    int l1 = getLight(b1);
                    int l2 = getLight(b2);
                    return l1-l2;
                }
            });
            BufferedImage bi = new BufferedImage(width*subImages.size()/2,height,BufferedImage.TYPE_INT_RGB);
            Graphics g = bi.getGraphics();
            // only consider every second char, since we only want 256 chars
            for (int i=0;i<subImages.size()/2;i++){
                g.drawImage(subImages.get(i*2),i*width,0,null);
            }
            g.dispose();
            ImageIO.write(bi,"png",new File(args[1]));
        }
        catch (Exception e){
            e.printStackTrace();
        }
    }
    public static BufferedImage getInverseImage(BufferedImage bufferedImage){
        BufferedImage copy =  new BufferedImage(bufferedImage.getWidth(),bufferedImage.getHeight(),BufferedImage.TYPE_INT_RGB);
        for (int x=0;x<copy.getWidth();x++){
            for (int y=0;y<copy.getHeight();y++){
                int rgb = bufferedImage.getRGB(x,y);
                int flippedRGB = 0xffffff ^ rgb;
                copy.setRGB(x,y,flippedRGB);
            }
        }
        return copy;
    }

    private static Map<BufferedImage,Integer> cache = new HashMap<BufferedImage, Integer>();
    private static int getLight(BufferedImage img){
        Integer res = cache.get(img);
        if (res != null){
            return res;
        }

        res = 0;
        final int white = -1;
        for (int i=0;i<img.getWidth();i++){
            for (int j=0;j<img.getHeight();j++){
                int rgb = img.getRGB(i,j);
                if (rgb!=white){
                    res++;
                }
            }
        }

        cache.put(img,res);
        return res;
    }
}